A roll bearing for a continuous hot dipping bath has generally been fashioned of a stainless steel, high-chromium steel, sintered carbide etc., having excellent properties with respect to corrosion resistance, and being formed through build-up welding or a sleeve type construction. However, these materials wear and can be damaged, for example, after about one week of immersion in a hot zinc dipping bath. As a result of the damage, a play results between a roll shaft and the roll bearing, and a roll and a hot dipping apparatus will oscillate, thereby adversely affecting the overall plating process.
It has been found that it is difficult to completely prevent corrosion of a metal due to molten metal even if the metal, employed is relatively excellent with respect to corrosion resistance, for example is a metal such as stainless steel, high-chromium steel or sintered carbide. Consequently, corrosion wear due to molten metal as well as friction is caused at the time of sliding of the roll bearing, thus increasing the wearing depth. It has also been determined that, when corrosion reaches a certain stage, corrosion pits are formed in the sliding surfaces of the roll shaft and bearing thereby promoting additional wear due to friction.
In order to decrease the wearing of the roll bearing, it is necessary to select a material which is excellent in corrosion resistance against molten metal. In this connection, some ceramics exhibit little corrosion due to molten metal, and such ceramics can be regarded as the optimum material for a roll bearing for a hot dipping bath.
In, for example, JP-A-3-177552, a bearing for a continuously operating hot dipping bath is proposed wherein a sintered ceramic member is closely fitted on the outer peripheral surface of a roll shaft through a metallic buffer material, and a solid lubricative ceramic material is provided on an inner peripheral surface of the bearing. Additional rolling bearings are proposed in JP-A-2-153055 and JP-A-1-159359, which bearings are fashioned of a ceramic material.
A disadvantage in the above proposed conventional approaches results in the fact that no consideration is given to a specific combination of the ceramic and necessary solid lubricant during actual operation in the continuous hot dipping bath.
In other words, it has been determined that although ceramics are excellent in corrosion resistance against molten metal, a new problem arises in that intermetallic compounds generated as a result of a reaction between the molten metal and metallic construction elements, such as a roll and a bearing, immersed in the molten metal adversely affect the solid lubricant.